1. Field of the Invention
This invention relates to a method and apparatus for increasing hydrocarbon production from heavy oil and bitumen reservoirs.
2. Description of the Related Art
Hydrocarbon production from heavy oil and bitumen reservoirs is commonly achieved through the use of a cyclic steam stimulation (CSS) process. In this process, individual wells are alternately used as steam injection wells and then as production wells. The steam is commonly injected into the same zone as the hydrocarbons are to be produced from, using a same set of perforations in the well casing.
A major drawback exists in any process using the same set of perfs for injection and production. Each time steam is injected into the perforations, oil just outside the perforations is pushed further away from the well by the steam, so that at the end of the injection, the reservoir adjacent to the perforations contains only irreducible oil and large quantities of steam and heat. When the well is put on production, it initially produces only water, steam, and heat, rather than the desired hydrocarbons. Well production is delayed until the oil can move back to the wellbore from farther out in the formation. As cumulative recovery from the well increases, the oil remaining to be recovered is farther and farther from the wellbore. The high heat production and delayed oil production make the currently used CSS process less and less efficient with time.
U.S. Pat. No. 3,994,341 to Anderson, et al. proposes a system for use in heavy oil reservoirs whereby two sets of perforations are separated by a thermal packer. An additional closed-loop flow path is extended past both sets of perforations and a hot fluid is run through the flow loop to facilitate injectivity of the upper perforations. The upper perforations are then injected with a hot drive fluid at the same time as hydrocarbons are produced through a tubing string from the lower set of perforations.
Two drawbacks are inherent in this method. First, it requires the use of a special closed loop flow path. There are several disadvantages to this. Running the flow path into the well takes a substantial amount of time, and, hence, is costly. Operation of the flow path is even more time consuming. Heat conduction is a slow process, adding a significant additional time delay before a well can be brought on production. This, again, is lost income. Finally, placing excess equipment downhole uses valuable space and increases the chance of mechanical problems with the well. The second drawback to this method is the poor efficiency achieved through simultaneous injection and production. Simultaneous injection and production decreases drive energy and increases coning. Thus production, when it occurs, is less efficient.